<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box1 {
      display: flex;
      /* flex-direction: row-reverse; */
      /* flex-direction: column; */
      flex-direction: column-reverse;
      width: 600px;
      height: 600px;
      background-color: red;
    }
    .box1 div {
      width: 100px;
      height: 100px;
      background-color: pink;
      margin: 5px;
    }
  </style>
</head>
<body>
  <div class="box1">
    <div>a</div>
    <div>b</div>
    <div>c</div>
  </div>
  <div class="box2">2</div>
  <div class="box3">3</div>
</body>
</html>